Linux is the major choice of operating system for most of the computers worldwide, particularly in servers. This is for many reasons, the most important one being free and open-source. Because this is open-source, communities can add features and logic on top of Linux, according to their taste and choice, while leaving the main Linux Kernel undisturbed.

Linux a shell, a Command Line Interface, known mostly as BASH(Bourne Again SHell). Although people have created many alternatives to this shell, the main language under the hood is mostly the same. The BASH accepts commands as user input and then executes it. Because, Linux is very common in cloud servers and work stations, it is essential to learn and practice important commands of BASH, in order to operate a task in Linux, in the most efficient manner as possible. In Linux, directories are the same as folders.

In Linux, the general syntax for a command is case-sensitive and as follows:
command [-flag(s)] [-option(s) [value]] [argument(s)]

Relative paths begin with no slashes but absolute paths begin with "/"

"." represents current directory, ".." represents one level above the current directory, "- represents the previous directory

1. View current working directory

   pwd
   e.g. pwd

2. Change working directory

   cd folder_name
   e.g. cd folder_2

3. Change to one level above the current directory

   cd ..
   e.g. cd ..

4. List down the contents of a directory

   ls
   e.g. ls

5. List down the contents of a directory in compact form

   ls -l
   e.g. ls -l

6. List down the contents of a directory, sorted by size

   ls -s

7. Output text on terminal

   echo text_here
   e.g. echo Hello World!

8. Create a directory

   mkdir folder_name
   e.g. mkdir folder 2

9. Create a file

   touch file_name
   e.g. touch file.txt

10. Copy file to a directory

    cp file_name folder_name
    e.g. cp hello.word folder2

11. Delete a file from a directory

    rm file_name
    e.g. rm hello.txt

12. Delete a directory (be careful when removing directories recursively, as it may potentially destroy the operating system)

    rm -r folder_name e.g. rm -r folder1

13. Move a file to a directory

    mv file_name folder_name
    e.g. mv hello.txt folder2

14. Rename a file

    mv file_name new_file_name
    e.g. mv hello.txt hello.word

15. View content of a file

    more file_name
    e.g. more hello.word

16. View the file tree of a directory

    find folder_name
    e.g. find folder3

17. Change to two levels above the current directory

    cd ../..

18. Change to a directory within another directory

    cd folder_name/other_folder_name
    e.g. cd folder1/folder2

19. View path of a file within a directory

    find -name file_name
    e.g. find -name hello.word

20. View path of a directory within a directory

    find -name file_name
    e.g. find -name folder2

21. Remove an empty directory

    rmdir folder_name
    e.g. rmdir folder3

22. Append output of echo command to a file

    echo Hello World! >> file_name
    e.g. echo Hello! >> hello.txt